SSR 431 connects the Chester-Hadlyme Ferry and Gillette Castle State Park with points to the north. It begins at Ferry Road (CT 148) in Hadlyme, just north of the ferry. It runs north for a short distance to the entrance to the park and then continues north until Town Street (CT 82) in East Haddam, where it ends. SSR 431 is a narrow, curvy two-lane road. It is known as Geer Hill Road in Hadlyme and as River Road in East Haddam.